1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device and a photomask, and in particular, to a method for manufacturing a semiconductor device and a photomask with an exposure technology of electron beams.
2. Description of the Related Art
In an electron-beam exposure device, a region for exposure is divided into a plurality of fields determined depending on a deflection width of a main deflector, the fields are divided into a plurality of sub-fields determined depending on a deflection width of a sub-deflector, electron beams for variable shaping are emitted every divided sub-field, and a pattern is exposed. Therefore, the connection accuracy of a connecting portion of the pattern over the sub-fields boundary, particularly, the connection accuracy of the pattern between the sub-fields belonging to adjacent fields is strict, and there is a problem of deterioration in resolution of the pattern at the sub-field boundary.
As a conventional method for improving the connection accuracy of the pattern over the sub-field boundary, there is proposed a method for generating an additional pattern at the connection portion as disclosed in Japanese Laid-open Patent Publication No. 6-13298 and a method for multiple-exposure by changing the boundary position of the field as disclosed in Japanese Laid-open Patent Publication No. 2002-170768.
Recent fine processing and high density of a semiconductor device (or a semiconductor element) causes problems of not only deterioration in connection accuracy of the pattern at the sub-field boundary due to an error of positional precision of the sub-field but also deterioration in resolution of a narrow space in the sub-field boundary. As the space between large patterns is narrower, the fog of the amount of exposure of electron beams due to back scattering from a substrate is large and the short-circuit can easily occur due to the positional deviation between the sub-fields.
However, the method for generating the additional pattern disclosed in Japanese Laid-open Patent Application Publication No. 6-13298 is not applied to space. Further, with the method for multiple-exposure disclosed in Japanese Laid-open Patent Publication No. 2002-170768, the positional deviation between the patterns affects the similar influence of blur of the electron beams, and the exposure margin of narrow space is reduced. Therefore, this method may not be used as much as possible. As mentioned above, the conventional methods have a problem that the deterioration of resolution of the narrow space cannot be certainly prevented.